demux: avoid a copy of demux packets with lavf, reduce padding

When demux_lavf read a new packet it used to copy the data from
libavformat's struct AVPacket to struct demux_packet and then free the
lavf packet. Change it to instead keep the AVPacket allocated and
point demux_packet fields to the buffer in that.

Also change MP_INPUT_BUFFER_PADDING_SIZE to 8 which matches
FF_INPUT_BUFFER_PADDING SIZE; demux_lavf packets won't have more
padding now anyway (it was increased from 8 earlier when
FF_INPUT_BUFFER_PADDING_SIZE was increased in libavcodec, but that
change was reverted).

libmpdemux/demux_lavf.c

@@ -743,10 +743,15 @@ static void check_internet_radio_hack(struct demuxer *demuxer)
     }
 }
 
+static int destroy_avpacket(void *pkt)
+{
+    av_free_packet(pkt);
+    return 0;
+}
+
 static int demux_lavf_fill_buffer(demuxer_t *demux, demux_stream_t *dsds)
 {
     lavf_priv_t *priv = demux->priv;
-    AVPacket pkt;
     demux_packet_t *dp;
     demux_stream_t *ds;
     int id;
@@ -754,8 +759,12 @@ static int demux_lavf_fill_buffer(demuxer_t *demux, demux_stream_t *dsds)
 
     demux->filepos = stream_tell(demux->stream);
 
-    if (av_read_frame(priv->avfc, &pkt) < 0)
+    AVPacket *pkt = talloc(NULL, AVPacket);
+    if (av_read_frame(priv->avfc, pkt) < 0) {
+        talloc_free(pkt);
         return 0;
+    }
+    talloc_set_destructor(pkt, destroy_avpacket);
 
     // handle any new streams that might have been added
     for (id = priv->nb_streams_last; id < priv->avfc->nb_streams; id++)
@@ -764,7 +773,7 @@ static int demux_lavf_fill_buffer(demuxer_t *demux, demux_stream_t *dsds)
 
     priv->nb_streams_last = priv->avfc->nb_streams;
 
-    id = pkt.stream_index;
+    id = pkt->stream_index;
 
     if (id == demux->audio->id || priv->internet_radio_hack) {
         // audio
@@ -787,39 +796,27 @@ static int demux_lavf_fill_buffer(demuxer_t *demux, demux_stream_t *dsds)
         ds = demux->sub;
         sub_utf8 = 1;
     } else {
-        av_free_packet(&pkt);
+        talloc_free(pkt);
         return 1;
     }
 
-    if (0 /*pkt.destruct == av_destruct_packet*/) {
+    dp = new_demux_packet_fromdata(pkt->data, pkt->size);
-        //ok kids, dont try this at home :)
+    dp->avpacket = pkt;
-        dp = malloc(sizeof(demux_packet_t));
-        dp->len = pkt.size;
-        dp->next = NULL;
-        dp->refcount = 1;
-        dp->master = NULL;
-        dp->buffer = pkt.data;
-        pkt.destruct = NULL;
-    } else {
-        dp = new_demux_packet(pkt.size);
-        memcpy(dp->buffer, pkt.data, pkt.size);
-        av_free_packet(&pkt);
-    }
 
-    int64_t ts = priv->use_dts ? pkt.dts : pkt.pts;
+    int64_t ts = priv->use_dts ? pkt->dts : pkt->pts;
     if (ts != AV_NOPTS_VALUE) {
         dp->pts = ts * av_q2d(priv->avfc->streams[id]->time_base);
         priv->last_pts = dp->pts * AV_TIME_BASE;
         // always set duration for subtitles, even if AV_PKT_FLAG_KEY isn't set,
         // otherwise they will stay on screen to long if e.g. ASS is demuxed
         // from mkv
-        if ((ds == demux->sub || (pkt.flags & AV_PKT_FLAG_KEY)) &&
+        if ((ds == demux->sub || (pkt->flags & AV_PKT_FLAG_KEY)) &&
-            pkt.convergence_duration > 0)
+            pkt->convergence_duration > 0)
-            dp->duration = pkt.convergence_duration *
+            dp->duration = pkt->convergence_duration *
                 av_q2d(priv->avfc->streams[id]->time_base);
     }
     dp->pos = demux->filepos;
-    dp->flags = !!(pkt.flags & AV_PKT_FLAG_KEY);
+    dp->flags = !!(pkt->flags & AV_PKT_FLAG_KEY);
     // append packet to DS stream:
     ds_add_packet(ds, dp);
     return 1;

libmpdemux/demuxer.c

@@ -176,7 +176,7 @@ const demuxer_desc_t *const demuxer_list[] = {
     NULL
 };
 
-struct demux_packet *new_demux_packet(size_t len)
+static struct demux_packet *create_packet(size_t len)
 {
     if (len > 1000000000) {
         mp_msg(MSGT_DEMUXER, MSGL_FATAL, "Attempt to allocate demux packet "
@@ -194,6 +194,13 @@ struct demux_packet *new_demux_packet(size_t len)
     dp->refcount = 1;
     dp->master = NULL;
     dp->buffer = NULL;
+    dp->avpacket = NULL;
+    return dp;
+}
+
+struct demux_packet *new_demux_packet(size_t len)
+{
+    struct demux_packet *dp = create_packet(len);
     dp->buffer = malloc(len + MP_INPUT_BUFFER_PADDING_SIZE);
     if (!dp->buffer) {
         mp_msg(MSGT_DEMUXER, MSGL_FATAL, "Memory allocation failure!\n");
@@ -203,6 +210,14 @@ struct demux_packet *new_demux_packet(size_t len)
     return dp;
 }
 
+// data must already have suitable padding
+struct demux_packet *new_demux_packet_fromdata(void *data, size_t len)
+{
+    struct demux_packet *dp = create_packet(len);
+    dp->buffer = data;
+    return dp;
+}
+
 void resize_demux_packet(struct demux_packet *dp, size_t len)
 {
     if (len > 1000000000) {
@@ -237,6 +252,9 @@ void free_demux_packet(struct demux_packet *dp)
     if (dp->master == NULL) {  //dp is a master packet
         dp->refcount--;
         if (dp->refcount == 0) {
+            if (dp->avpacket)
+                talloc_free(dp->avpacket);
+            else
                 free(dp->buffer);
             free(dp);
         }

libmpdemux/demuxer.h

@@ -122,7 +122,8 @@ enum timestamp_type {
 #define SEEK_FORWARD  (1 << 2)
 #define SEEK_BACKWARD (1 << 3)
 
-#define MP_INPUT_BUFFER_PADDING_SIZE 64
+// demux_lavf can pass lavf buffers using FF_INPUT_BUFFER_PADDING_SIZE instead
+#define MP_INPUT_BUFFER_PADDING_SIZE 8
 
 // Holds one packet/frame/whatever
 typedef struct demux_packet {
@@ -136,6 +137,7 @@ typedef struct demux_packet {
     int refcount; // counter for the master packet, if 0, buffer can be free()d
     struct demux_packet *master; //in clones, pointer to the master packet
     struct demux_packet *next;
+    struct AVPacket *avpacket;   // original libavformat packet (demux_lavf)
 } demux_packet_t;
 
 typedef struct demux_stream {
@@ -302,6 +304,8 @@ typedef struct {
 } demux_program_t;
 
 struct demux_packet *new_demux_packet(size_t len);
+// data must already have suitable padding
+struct demux_packet *new_demux_packet_fromdata(void *data, size_t len);
 void resize_demux_packet(struct demux_packet *dp, size_t len);
 struct demux_packet *clone_demux_packet(struct demux_packet *pack);
 void free_demux_packet(struct demux_packet *dp);